The invention relates to rigid or flexible substrates covered with a thin coating of diamond-like material which thereby render the substrate surfaces i.a. very hard, corrosion and wear resistant and self-lubricating at the same time. The invention relates also to certain vacuum processes for coating the substrates.
It is generally known to coat substrates with films of diamond-like carbon. Diamond-Like Carbon (DLC) films are amorphous hydrogenated carbon films (a-C:H) that display high hardness and high elasticity combined with good corrosion protection, chemical inertness and a smooth surface. These properties make these films feasible for industrial applications such as hard, wear resistant, self lubricating and corrosion resistant coatings.
However, DLC films show several drawbacks that impede their successful commercial introduction. The most important practical problem is the difficult adhesion to several substrates, particularly steel substrates. This difficulty is caused by the high compressive residual stresses, up to several GPa, present in the material. Other disadvantages are the low thermal stability. limiting the working temperature to about 300.degree. C., the low transmission for visible light and the increase of the coefficient of friction with increasing air humidity. Doping DLC with both metals (Ti, Zr, W, Nb, Ta) and non-metallic elements (Si, F, O, B, N) favourably influences many properties but generally lowers the hardness. Likewise, the interposition of Si, SiO or metal (Al, Ti) between the substrate and a DLC-layer, although improving its adhesion to the substrate, provides only for a soft interface.
It is also known from U.S. Pat. No. 5,352,493 to coat substrates with certain diamond-like nanocomposite compositions (DLN). Diamond-Like Nanocomposite coatings consist of an amorphous structure, comprising generally two interpenetrating networks a-C:H and a-Si:O: DLN, or Dylyn.TM.. DLN exhibits several attractive properties when compared with Diamond-Like Carbon (a-C:H, DLC). Besides the higher temperature stability, the retaining of mechanical properties upon doping with metals and the low internal stress facilitating adhesion. the very low coefficient of friction (&lt;0.1). often even in humid air and under water, is of prime importance for many industrial tribological applications.
However, with the present state-of-the-art deposition technology for DLN using a liquid polyphenylmethylsiloxane precursor, the hardness of the DLN coatings, as measured by depth-sensing indentation. varies generally between 12 GPa and 17 GPa. For several applications. such as abrasive applications, situations of impact erosion or severe tribological applications. this hardness value may be insufficient. In those cases. a hardness of 20 to 25 GPa may be desirable.